The medium contains a nutrient base of peptone and beef extract, along with glucose (dextrose) as a fermentable carbohydrate and two pH indicators, bromocresol purple and cresol red. When the medium is inoculated with a glucose-fermenting organism, acid is produced, changing the color from purple to yellow. The resulting acidic environment stimulates the production of decarboxylase enzymes (if the specific amino acid is added). If the organism decarboxylates the amino acid, alkaline diamines are formed, which raises the pH and returns the medium to its original purple color. If the organism does not produce the enzyme, the medium remains yellow.
Advantages
- Sharp Color Transitions: The dual indicator system (bromocresol purple and cresol red) provides clear, unmistakable color changes for easier reading.
- High Sensitivity: Optimized for the detection of even weak decarboxylase activity in various enteric species.
- NutriSelect® Plus Quality: Premium-grade ingredients ensure consistent performance and reliable biochemical profiles from batch to batch.
- Versatile Base: Can be supplemented with different amino acids (Lysine, Arginine, or Ornithine) to perform a complete differentiation battery.
- Standardized Reference: Formulated according to the original Moeller specifications for biochemical identification.
Interpretation of Results
| Reaction |
Appearance |
Interpretation |
| Positive (+) |
Purple / Violet |
Decarboxylation occurred (alkaline) |
| Negative (-) |
Yellow |
Glucose fermentation only (acidic) |
| Control |
Purple to Yellow |
Standard reaction for glucose-fermenting organisms |
Technical specifications
| Catalogue number |
D2935 |
| Brand / Product Line |
Sigma-Aldrich / NutriSelect® Plus |
| Typical Composition (g/L) |
Peptic digest of animal tissue (5.0); Beef extract (5.0); Dextrose (0.5); Bromocresol purple (0.01); Cresol red (0.005); Pyridoxal (0.005) |
| pH (at 25 °C) |
6.0 ± 0.2 |
| Preparation |
10.52 g/L |
| Storage Temperature |
15 – 25 °C |
Available packaging options
| D2935-500G |
500 g plastic bottle |
